THE FLOWER--ITS PARTS AND FORMS
The function of the flower is to _produce seed_. It is probable that
all its varied forms and colors contribute to this supreme end. These
forms and colors please the human fancy and add to the joy of living,
but the flower exists for the good of the plant, not for the good of
man. The parts of the flower are of two general kinds--those that are
directly concerned in the _production of seeds_, and those that act as
_covering and protecting organs_. The former parts are known as the
=essential organs=; the latter as the =floral envelopes=.
=Envelopes.=--The floral envelopes usually bear a close resemblance to
leaves. These envelopes are very commonly of two series or kinds--the
_outer_ and the _inner_. The outer series, known as the =calyx=, is
usually smaller and green. It usually comprises the outer cover of the
flower bud. The calyx is the lowest whorl in Fig. 173.
[Illustration: FIG. 173.--FLOWER OF A BUTTERCUP IN SECTION.]
The inner series, known as the =corolla=, is usually colored and more
special or irregular in shape than the calyx. It is the showy part of
the flower, as a rule. The corolla is the second or large whorl in Fig.
173.
The _calyx_ may be composed of several leaves. Each leaf is a =sepal=.
If it is of one piece, it may be lobed or divided, in which case the
divisions are called =calyx-lobes=.
In like manner, the corolla may be composed of =petals=, or it
may be of one piece and variously lobed. A calyx of one piece, no
matter how deeply lobed, is =gamosepalous=. A corolla of one piece
is =gamopetalous=. When these series are of separate pieces, as in
Fig. 173, the flower is said to be =polysepalous= and =polypetalous=.
Sometimes both series are of separate parts, and sometimes only one of
them is so formed.
_The floral envelopes are homologous with leaves._ Sepals and petals,
at least when more than three or five, are in more than one whorl, and
one whorl stands below another so that the parts overlap. They are
borne on the expanded or thickened end of the flower stalk; this end
is the =torus=. In Fig. 173 all the parts are seen as attached to the
torus. This part is sometimes called the _receptacle_, but this word is
a common-language term of several meanings, whereas torus has no other
meaning. Sometimes one part is attached to another part, as in the
fuchsia (Fig. 174), in which the petals are borne on the calyx-tube.
[Illustration: FIG. 174.--FLOWER OF FUCHSIA IN SECTION.]
=Subtending Parts.=--Sometimes there are _leaf-like parts just
below the calyx_, looking like a second calyx. Such parts accompany
the carnation flower. These parts are =bracts= (bracts are small
specialized leaves); and they form an =involucre=. We must be careful
that we do not mistake them for true flower parts. Sometimes the bracts
are large and petal-like, as in the great white blooms of the flowering
dogwood: here the real flowers are several, small and greenish, forming
a small cluster in the center.
=Essential Organs.=--The essential organs are of two series. The outer
series is composed of the =stamens=. The inner series is composed of
the =pistils=.
_Stamens_ bear the =pollen=, which is made up of grains or spores, each
spore usually being a single plant cell. The stamen is of two parts,
as is readily seen in Figs. 173, 174,--the enlarged terminal part or
=anther=, and the stalk or =filament=. The filament is often so short
as to seem to be absent, and the anther is then said to be _sessile_.
The anther bears the pollen spores. It is made up of two or four parts
(known as sporangia or spore-cases), which burst and discharge the
pollen. _When the pollen is shed, the stamen dies._
The _pistil has three parts_: the lowest, or seed-bearing part, which
is the =ovary=; the =stigma= at the upper extremity, which is a
flattened or expanded surface, and usually roughened or sticky; the
stalk-like part or =style=, connecting the ovary and stigma. Sometimes
the style is apparently wanting, and the stigma is said to be sessile
on the ovary. These parts are shown in the fuchsia (Fig. 174). The
ovary or seed vessel is at _a_. A long style, bearing a large stigma,
projects from the flower. See also Figs. 175 and 176.
[Illustration: FIG. 175.--THE STRUCTURE OF A PLUM BLOSSOM.
_se_, sepals; _p_, petals; _sta_, stamens; _o_, ovary; _s_, style;
_st_, stigma. The pistil consists of the ovary, style, and stigma. It
contains the seed part. The stamens are tipped with anthers, in which
the pollen is borne. The ovary, _o_, ripens into the fruit.]
Stamens and pistils probably are homologous with leaves. A pistil is
sometimes conceived to represent anciently a leaf as if rolled into a
tube; and an anther, a leaf of which the edges may have been turned in
on the midrib.
[Illustration: FIG. 176.--SIMPLE PISTILS OF BUTTERCUP, one in
longitudinal section.]
The pistil may be of _one part or compartment, or of many parts_. The
different units or parts of which it is composed are =carpels=. Each
carpel is homologous with a leaf. Each carpel bears one or more seeds.
A pistil of one carpel is =simple=; of two or more carpels, =compound=.
Usually the structure of the pistil may be determined by cutting
horizontally across the lower or seed-bearing part, as Figs. 177, 178
explain. A flower may contain a simple pistil (one carpel), as the pea
(Fig. 177); _several simple pistils_ (several separate carpels), as
the buttercup (Fig. 176); or a _compound pistil_ with carpels united,
as the Saint John’s wort (Fig. 178) and apple. How many carpels in an
apple? A peach? An okra pod? A bean pod? The seed cavity in each carpel
is called a =locule= (Latin _locus_, a place). In these locules _the
seeds are borne_.
[Illustration: FIG. 177.--PISTIL OF GARDEN PEA, the stamens being
pulled down in order to disclose it; also a section showing the single
compartment (compare Fig. 188).]
[Illustration: FIG. 178.--COMPOUND PISTIL OF A ST. JOHN’S WORT. It has
5 carpels.]
=Conformation of the Flower.=--A flower that has calyx, corolla,
stamens, and pistils is said to be =complete= (Fig. 173); all others
are =incomplete=. In some flowers both the floral envelopes are
wanting: such are =naked=. When one of the floral envelope series is
wanting, the remaining series is said to be calyx, and the flower
is therefore =apetalous= (without petals). The knotweed (Fig. 179),
smartweed, buckwheat, elm are examples.
[Illustration: FIG. 179.--KNOTWEED, a very common but inconspicuous
plant along hard walks and roads. Two flowers, enlarged, are shown at
the right. These flowers are very small and borne in the axils of the
leaves.]
Some flowers lack the pistils: these are =staminate=, whether the
envelopes are missing or not. Others lack the stamens: these are
=pistillate=. Others have neither stamens nor pistils: these are
=sterile= (snowball and hydrangea). Those that have both stamens and
pistils are =perfect=, whether or not the envelopes are missing. Those
that lack either stamens or pistils are =imperfect= or =diclinous=.
Staminate and pistillate flowers are imperfect or diclinous.
[Illustration: FIG. 180.--STAMINATE CATKINS OF OAK. The pistillate
flowers are in the leaf axils, and not shown in this picture.]
[Illustration: FIG. 181.--BEGONIA FLOWERS.
Staminate at _A_; pistillate below, with the winged ovary at _B_.]
When staminate and pistillate flowers are borne on the same plant,
_e.g._ oak (Fig. 180), corn, beech, chestnut, hazel, walnut, hickory,
pine, begonia (Fig. 181), watermelon, gourd, pumpkin, the plant is
=monœcious= (“in one house”). When they are on different plants,
_e.g._ poplar, cottonwood, bois d’arc, willow (Fig. 182), the plant is
=diœcious= (“in two houses”). Some varieties of strawberry, grape, and
mulberry are partly diœcious. Is the rose either monœcious or diœcious?
[Illustration: FIG. 182.--CATKINS OF A WILLOW.
A staminate flower is shown at _s_, and a pistillate flower at _p_. The
staminate and pistillate are on different plants.]
[Illustration: FIG. 183.--FLOWER OF GARDEN NASTURTIUM.
Separate petal at _a_. The calyx is produced into a spur.]
[Illustration: FIG. 184.--THE FIVE PETALS OF THE PANSY, detached to
show the form.]
[Illustration: FIG. 185.--FLOWER OF CATNIP.]
Flowers in which the parts of each series are alike are said to be
=regular= (as in Figs. 173, 174, 175). Those in which some parts are
unlike other parts of the same series are =irregular=. Their regularity
may be in calyx, as in nasturtium (Fig. 183); in corolla (Figs. 184,
185); in the stamens (compare nasturtium, catnip, Fig. 185, sage); in
the pistils. Irregularity is most frequent in the corolla.
=Various Forms of Corolla.=--The corolla often assumes very definite
or distinct forms, especially when gamopetalous. It may have a long
tube with a wide-flaring limb, when it is said to be =funnelform=,
as in morning-glory and pumpkin. If the tube is very narrow and the
limb stands at right angles to it, the corolla is =salverform=, as in
phlox. If the tube is very short and the limb wide-spreading and nearly
circular in outline, the corolla is =rotate= or =wheel-shaped=, as in
potato.
A gamopetalous corolla or gamosepalous calyx is often cleft in such
way as to make two prominent parts. Such parts are said to be =lipped=
or =labiate=. Each of the lips or lobes may be notched or toothed. In
5-membered flowers, the lower lip is usually 3-lobed and the upper one
2-lobed. Labiate flowers are characteristic of the mint family (Fig.
185), and the family therefore is called the Labiatæ. (Literally,
labiate means merely “lipped,” without specifying the number of lips or
lobes; but it is commonly used to designate 2-lipped flowers.) Strongly
2-parted polypetalous flowers may be said to be labiate; but the term
is oftenest used for gamopetalous corollas.
Labiate gamopetalous flowers that are closed in the throat (or entrance
to the tube) are said to be grinning or =personate= (personate means
_masked_, or _person-like_). Snap-dragon is a typical example;
also toadflax or butter-and-eggs (Fig. 186), and many related
plants. Personate flowers usually have definite relations to insect
pollination. Observe how an insect forces his head into the closed
throat of the toadflax.
[Illustration: FIG. 186.--PERSONATE FLOWER OF TOADFLAX.]
The peculiar flowers of the pea tribes are explained in Figs. 187, 188.
[Illustration: FIG. 187.--FLOWERS OF THE COMMON BEAN, with one flower
opened (_a_) to show the structure.]
[Illustration: FIG. 188.--DIAGRAM OF ALFALFA FLOWER IN SECTION:
_C_, calyx; _D_, standard; _W_, wing; _K_, keel; _T_, stamen-tube; _F_,
filament of tenth stamen; _X_, stigma; _Y_, style; _O_, ovary; the
dotted lines at _E_ show position of stamen tube, when pushed upward by
insects. Enlarged.]
=Spathe Flowers.=--In many plants, very simple (often naked) flowers
are borne in dense, more or less fleshy spikes, and the spike is
inclosed in or attended by a leaf, sometimes corolla-like, known as a
=spathe=. The spike of flowers is technically known as a =spadix=. This
type of flower is characteristic of the great arum family, which is
chiefly tropical. The commonest wild representatives in the North are
Jack-in-the-pulpit, or Indian turnip, and skunk cabbage. In the former
the flowers are all diclinous and naked. In the skunk cabbage all the
flowers are perfect and have four sepals. The common calla is a good
example of this type of inflorescence.
[Illustration: FIG. 189.--HEAD OF SUNFLOWER.]
=Compositous Flowers.=--The head (anthodium) or so-called “flower” of
sunflower (Fig. 189), thistle, aster, dandelion, daisy, chrysanthemum,
goldenrod, _is composed of several or many little flowers, or_
=florets=. These florets are inclosed in a more or less dense and
usually green _involucre_. In the thistle (Fig. 190) this involucre is
prickly. A longitudinal section discloses the florets, all attached at
bottom to a common torus, and densely packed in the involucre. The pink
tips of these florets constitute the showy part of the head.
[Illustration: FIG. 190.--LONGITUDINAL SECTION OF THISTLE HEAD; also a
FLORET OF THISTLE.]
Each floret of the thistle (Fig. 190) is a complete flower. At _a_ is
the ovary. At _b_ is a much-divided plumy calyx, known as the =pappus=.
The corolla is long-tubed, rising above the pappus, and is enlarged and
5-lobed at the top, _c_. The style projects at _e_. The five anthers
are united about the style in a ring at _d_. Such anthers are said to
be =syngenesious=. These are the various parts of the florets of the
Compositæ. In some cases the pappus is in the form of barbs, bristles,
or scales, and sometimes it is wanting. The pappus, as we shall see
later, assists in distributing the seed. Often the florets are not
all alike. The corolla of those in the outer circles may be developed
into a _long, straplike, or tubular part_, and the head then has the
appearance of being one flower with a border of petals. Of such is
the sunflower (Fig. 189), aster, bachelor’s button or cornflower, and
field daisy (Fig. 211). These long corolla-limbs are called rays. In
some cultivated composites, all the florets may develop =rays=, as in
the dahlia and chrysanthemum. In some species, as dandelion, all the
florets naturally have rays. Syngenesious arrangement of anthers is the
most characteristic single feature of the composites.
[Illustration: FIG. 191.--PETALS ARISING FROM THE STAMINAL COLUMN OF
HOLLYHOCK, and accessory petals in the corolla-whorl.]
=Double Flowers.=--Under the stimulus of cultivation and increased
food supply, flowers tend to become double. True doubling arises in
two ways, morphologically: (1) _stamens or pistils may produce petals_
(Fig. 191); (2) _adventitious or accessory petals may arise in the
circle of petals_. Both of these categories may be present in the
same flower. In the full double hollyhock the petals derived from
the staminal column are shorter and make a rosette in the center of
the flower. In Fig. 192 is shown the doubling of a daffodil by the
modification of stamens. Other modifications of flowers are sometimes
known as doubling. For example, double dahlias, chrysanthemums, and
sunflowers are forms in which the disk flowers have developed rays. The
snowball is another case. In the wild snowball the external flowers
of the cluster are large and sterile. In the cultivated plant all the
flowers have become large and sterile. Hydrangea is a similar case.
[Illustration: FIG. 192.--NARCISSUS OR DAFFODIL. Single flower at the
right.]
SUGGESTIONS.--=145.= If the pupil has been skillfully conducted
through this chapter _by means of careful study of specimens_ rather
than as a mere memorizing process, he will be in mood to challenge
any flower that he sees and to make an effort to understand it.
Flowers are endlessly modified in form; but they can be understood if
the pupil looks first for the anthers and ovaries. How may anthers
and ovaries always be distinguished? =146.= It is excellent practice
to find the flowers in plants that are commonly known by name, and to
determine the main points in their structure. What are the flowers in
Indian corn? pumpkin or squash? celery? cabbage? potato? pea? tomato?
okra? cotton? rhubarb? chestnut? wheat? oats? =147.= Do all forest
trees have flowers? Explain. =148.= Name all the monœcious plants you
know. Diœcious. =149.= What plants do you know that bloom before the
leaves appear? Do any bloom after the leaves fall? =150.= Explain the
flowers of marigold, hyacinth, lettuce, clover, asparagus, garden
calla, aster, locust, onion, burdock, lily-of-the-valley, crocus,
Golden Glow rudbeckia, cowpea. =151.= Define a _flower_.
NOTE TO THE TEACHER.--It cannot be urged too often that _the
specimens themselves_ be studied. If this chapter becomes a mere
recitation on names and definitions, the exercise will be worse than
useless. Properly taught by means of the flowers themselves, the
names become merely incidental and a part of the pupil’s language,
and the subject has living interest.